In a semiconductor device having multilayer interconnection such as LSI (large-scale integration) or the like, a low-k insulating film is often used as an interlayer insulating film between metal wirings. As for the low-k insulating film, a SiCO film having a dielectric constant of about 2.6 is used (see, e.g., Japanese Patent Application Publication No. 2012-74608).
The SiCO film has a porous structure and a high hygroscopic property. Therefore, in the case of using the SiCO film as the low-k insulating film, the low-k insulating film may absorb moisture and deteriorate. In order to prevent the SiCO film from absorbing moisture, the surface of the SiCO film is covered by an etching stop film such as a SiC film, a SiCN film or the like. Since, however, SiC or SiCN has a high dielectric constant of about 4 to 5, the dielectric constant of the entire interlayer insulating film including the SiCO film and the etching stop film is also increased.
To that end, recently, a CF (fluorocarbon) film is used as the low-k film. The CF film hardly absorbs moisture and has a low dielectric constant of about 2.2. Therefore, it is not required to cover the surface of the CF film by the etching stop film. As a result, it is possible to suppress the increase of the dielectric constant of the entire interlayer insulating film.
In the semiconductor device, the interlayer insulating film is formed to be in contact with a metal wiring, e.g., a copper wiring. In the case of using the CF film as the interlayer insulating film, the CF film is formed by plasma CVD using a CF-based gas. A physical adsorption force of moisture to copper is strong and, thus, moisture 41 exists on a copper wiring 40 during the plasma CVD (see FIG. 4A). Copper reacts with the moisture 41, fluorine radical in the plasma generated from the CF-based gas, and oxygen in an atmosphere. As a result, the surface of the copper wiring 40 is fluorinated and a fluoride 42 is generated (see FIG. 4B). The fluoride 42 increases a resistance of the copper wiring 40 and causes peeling off of the copper wiring 40 and the interlayer insulating film 43 (see FIG. 4C).
In order to suppress the formation of the fluoride, the moisture on the copper wiring is removed by heating a semiconductor wafer having semiconductor devices formed thereon using a heater or the like before the interlayer insulating film is formed.
However, in the case of evaporating the moisture on the copper wiring by heating the semiconductor wafer by the heater, the entire semiconductor wafer is heated by the heater. Therefore, the heating efficiency for removing the moisture is poor and it takes a long time, e.g., 15 minutes or more to remove the moisture. As a result, a throughput is decreased.